Purpose The purpose of this study was to explore and describe the process of illness adaptation of patients with Atrial Fibrillation (AF). Methods Data were collected from December 2017 to July 2018 through individual in-depth interviews with thirteen patients with AF. Verbatim transcripts were analyzed using the grounded theory methodology developed by Corbin and Strauss. Results The core category about the illness adaptation process of patients with AF was identified as “living a life managing the silent insurrection of the heart.” The process of illness adaptation of patients with AF consisted of four phases: “withdrawal”, “transition”, “practice”, and “adeptness”. Conclusion An in-depth understanding of the illness adaptation process of patients with AF will guide nurses in proactively developing and implementing effective nursing interventions to better support patients with AF in Korea.